Existing magnetic disk devices receive data from host systems with an approximately constant data size. Therefore, when data is sequentially stored in a buffer memory such as an SDRAM, an existing magnetic disk device easily searches for where in the buffer memory data is stored based on the initial address of the stored data.
Currently, a magnetic disk device having a compression circuit related to be stored data is considered. In the magnetic disk device having the compression circuit, as the compression ratio differs depending on the data type, the data size may vary according to the compressed data. Therefore, when compressed data is sequentially stored in the buffer memory of the magnetic disk device, it is difficult to search for where compressed data is stored.